Over four parts, Murder in the Valleys tells the story behind the biggest murder investigation in Welsh history and its enduring repercussions. One night in June 1999, three generations of a family were brutally killed in the small village of Clydach, South Wales. For more than twenty years, despite the conviction of a local builder, the case has divided the community. Filmed over 12 months, as the police decide it is time to review the evidence, this series examines a case that didn't end with the guilty verdict.